Encryption and Decryption of String according to given technique

Last Updated : 27 Dec, 2022

Given a string S, the task is to encrypt the string and decrypt the string again to the original form.
Encryption Technique: If L is the length of the string, then take two values, one the ceil of ?L (say b), and the other floor of ?L (say a), and make a two-dimensional matrix having rows = a, and columns = b.
If rows*columns < L, then increase the value of a or b, whichever is minimum. Fill the matrix with the characters of the original string sequentially. After obtaining the matrix, read the matrix column-wise and print the obtained string.

Decryption Technique: If L is the length of the encrypted string, then again find the two values a and b, where a is the ceil value of the ?L and b is the floor value of the ?L. Similarly create a 2D Matrix in which store the string column-wise and read the matrix row-wise to get the string in the original form.

Encryption Approach:

Find the length L of the string.
Find the ceil and floor values of ?Length and assign them to the variables.
Check if the product of the two variables >= Length, if not then increments the variable having a lesser value by 1.
Create a 2D matrix and fill the characters of the string row-wise.
Read the matrix column-wise to get the encrypted string.

Decryption Approach:

Find the length L of the string.
Find the ceil and floor values of ?Length and assign them to the variables.
Create a 2D matrix and fill the matrix by characters of string column-wise.
Read the matrix row-wise to get the decrypted string.

Below is the implementation of the above approach:

C++

// C++ implementation for Custom
// Encryption and Decryption of String

#include <bits/stdc++.h>
using namespace std;

// Function to encrypt the string
string encryption(string s)
{
    int l = s.length();
    int b = ceil(sqrt(l));
    int a = floor(sqrt(l));
    string encrypted;
    if (b * a < l) {
        if (min(b, a) == b) {
            b = b + 1;
        }
        else {
            a = a + 1;
        }
    }

    // Matrix to generate the 
    // Encrypted String
    char arr[a][b];
    memset(arr, ' ', sizeof(arr));
    int k = 0;
    
    // Fill the matrix row-wise
    for (int j = 0; j < a; j++) {
        for (int i = 0; i < b; i++) {
            if (k < l){
                arr[j][i] = s[k];
            }
            k++;
        }
    }

    // Loop to generate 
    // encrypted string
    for (int j = 0; j < b; j++) {
        for (int i = 0; i < a; i++) {
            encrypted = encrypted + 
                         arr[i][j];
        }
    }
    return encrypted;
}

// Function to decrypt the string
string decryption(string s){
    int l = s.length();
    int b = ceil(sqrt(l));
    int a = floor(sqrt(l));
    string decrypted;

    // Matrix to generate the 
    // Encrypted String
    char arr[a][b];
    memset(arr, ' ', sizeof(arr));
    int k = 0;
    
    // Fill the matrix column-wise
    for (int j = 0; j < b; j++) {
        for (int i = 0; i < a; i++) {
            if (k < l){
                arr[j][i] = s[k];
            }
            k++;
        }
    }

    // Loop to generate 
    // decrypted string
    for (int j = 0; j < a; j++) {
        for (int i = 0; i < b; i++) {
            decrypted = decrypted + 
                         arr[i][j];
        }
    }
    return decrypted;
}

// Driver Code
int main()
{
    string s = "Geeks For Geeks";
    string encrypted;
    string decrypted;
    
    // Encryption of String
    encrypted = encryption(s);
    cout << encrypted << endl;
    
    // Decryption of String
    decrypted = decryption(encrypted);
    cout << decrypted;
    return 0;
}

Java

// Java implementation for Custom
// Encryption and Decryption of String
class GFG
{

// Function to encrypt the String
static String encryption(char[] s)
{
    int l = s.length;
    int b = (int) Math.ceil(Math.sqrt(l));
    int a = (int) Math.floor(Math.sqrt(l));
    String encrypted = "";
    if (b * a < l)
    {
        if (Math.min(b, a) == b) 
        {
            b = b + 1;
        }
        else
        {
            a = a + 1;
        }
    }

    // Matrix to generate the 
    // Encrypted String
    char [][]arr = new char[a][b];
    int k = 0;
    
    // Fill the matrix row-wise
    for (int j = 0; j < a; j++) 
    {
        for (int i = 0; i < b; i++) 
        {
            if (k < l)
            {
                arr[j][i] = s[k];
            }
            k++;
        }
    }

    // Loop to generate 
    // encrypted String
    for (int j = 0; j < b; j++) 
    {
        for (int i = 0; i < a; i++) 
        {
            encrypted = encrypted + 
                        arr[i][j];
        }
    }
    return encrypted;
}

// Function to decrypt the String
static String decryption(char []s)
{
    int l = s.length;
    int b = (int) Math.ceil(Math.sqrt(l));
    int a = (int) Math.floor(Math.sqrt(l));
    String decrypted="";

    // Matrix to generate the 
    // Encrypted String
    char [][]arr = new char[a][b];
    int k = 0;
    
    // Fill the matrix column-wise
    for (int j = 0; j < b; j++) 
    {
        for (int i = 0; i < a; i++) 
        {
            if (k < l)
            {
                arr[j][i] = s[k];
            }
            k++;
        }
    }

    // Loop to generate 
    // decrypted String
    for (int j = 0; j < a; j++) 
    {
        for (int i = 0; i < b; i++) 
        {
            decrypted = decrypted + 
                        arr[i][j];
        }
    }
    return decrypted;
}

// Driver Code
public static void main(String[] args)
{
    String s = "Geeks For Geeks";
    String encrypted;
    String decrypted;
    
    // Encryption of String
    encrypted = encryption(s.toCharArray());
    System.out.print(encrypted +"\n");
    
    // Decryption of String
    decrypted = decryption(encrypted.toCharArray());
    System.out.print(decrypted);
}
}

// This code is contributed by PrinciRaj1992

Python3

# Python3 implementation for Custom
# Encryption and Decryption of String
from math import ceil,floor,sqrt

# Function to encrypt the
def encryption(s):
    l = len(s)
    b = ceil(sqrt(l))
    a = floor(sqrt(l))
    encrypted=""
    if (b * a < l):
        if (min(b, a) == b):
            b = b + 1
        else:
            a = a + 1

    # Matrix to generate the
    # Encrypted String
    arr = [[' ' for i in range(a)] for j in range(b)]
    k = 0

    # Fill the matrix row-wise
    for j in range(a):
        for i in range(b):
            if (k < l):
                arr[j][i] = s[k]
            k += 1

    # Loop to generate
    # encrypted
    for j in range(b):
        for i in range(a):
            encrypted = encrypted + arr[i][j]

    return encrypted

# Function to decrypt the
def decryption(s):
    l = len(s)
    b = ceil(sqrt(l))
    a = floor(sqrt(l))
    decrypted=""

    # Matrix to generate the
    # Encrypted String
    arr = [[' ' for i in range(a)] for j in range(b)]
    k = 0

    # Fill the matrix column-wise
    for j in range(b):
        for i in range(a):
            if (k < l):
                arr[j][i] = s[k]
            k += 1

    # Loop to generate
    # decrypted
    for j in range(a):
        for i in range(b):
            decrypted = decrypted + arr[i][j]
    return decrypted

# Driver Code

s = "Geeks For Geeks"
encrypted=""
decrypted=""

# Encryption of String
encrypted = encryption(s)
print(encrypted)

# Decryption of String
decrypted = decryption(encrypted)
print(decrypted)

# This code is contributed by mohit kumar 29

// C# implementation for Custom
// Encryption and Decryption of String
using System;

class GFG
{
 
// Function to encrypt the String
static String encryption(char[] s)
{
    int l = s.Length;
    int b = (int) Math.Ceiling(Math.Sqrt(l));
    int a = (int) Math.Floor(Math.Sqrt(l));
    String encrypted = "";
    if (b * a < l)
    {
        if (Math.Min(b, a) == b) 
        {
            b = b + 1;
        }
        else
        {
            a = a + 1;
        }
    }
 
    // Matrix to generate the 
    // Encrypted String
    char [,]arr = new char[a, b];
    int k = 0;
     
    // Fill the matrix row-wise
    for (int j = 0; j < a; j++) 
    {
        for (int i = 0; i < b; i++) 
        {
            if (k < l)
            {
                arr[j, i] = s[k];
            }
            k++;
        }
    }
 
    // Loop to generate 
    // encrypted String
    for (int j = 0; j < b; j++) 
    {
        for (int i = 0; i < a; i++) 
        {
            encrypted = encrypted + 
                        arr[i, j];
        }
    }
    return encrypted;
}
 
// Function to decrypt the String
static String decryption(char []s)
{
    int l = s.Length;
    int b = (int) Math.Ceiling(Math.Sqrt(l));
    int a = (int) Math.Floor(Math.Sqrt(l));
    String decrypted="";
 
    // Matrix to generate the 
    // Encrypted String
    char [,]arr = new char[a, b];
    int k = 0;
     
    // Fill the matrix column-wise
    for (int j = 0; j < b; j++) 
    {
        for (int i = 0; i < a; i++) 
        {
            if (k < l)
            {
                arr[j, i] = s[k];
            }
            k++;
        }
    }
 
    // Loop to generate 
    // decrypted String
    for (int j = 0; j < a; j++) 
    {
        for (int i = 0; i < b; i++) 
        {
            decrypted = decrypted + 
                        arr[i, j];
        }
    }
    return decrypted;
}
 
// Driver Code
public static void Main(String[] args)
{
    String s = "Geeks For Geeks";
    String encrypted;
    String decrypted;
     
    // Encryption of String
    encrypted = encryption(s.ToCharArray());
    Console.Write(encrypted +"\n");
     
    // Decryption of String
    decrypted = decryption(encrypted.ToCharArray());
    Console.Write(decrypted);
}
}

// This code is contributed by PrinciRaj1992

JavaScript

<script>

// JavaScript implementation for Custom
// Encryption and Decryption of let


// Function to encrypt the let
function encryption(s) {
    let l = s.length;
    let b = Math.ceil(Math.sqrt(l));
    let a = Math.floor(Math.sqrt(l));
    let encrypted = '';
    if (b * a < l) {
        if (Math.min(b, a) == b) {
            b = b + 1;
        }
        else {
            a = a + 1;
        }
    }

    // Matrix to generate the
    // Encrypted let
    let arr = new Array();

    for (let i = 0; i < a; i++) {
        let temp = [];
        for (let j = 0; j < b; j++) {
            temp.push([])
        }
        arr.push(temp)
    }

    for (let i = 0; i < a; i++) {
        for (let j = 0; j < b; j++) {
            arr[i][j] = " "
        }
    }


    let k = 0;

    // Fill the matrix row-wise
    for (let j = 0; j < a; j++) {
        for (let i = 0; i < b; i++) {
            if (k < l) {
                arr[j][i] = s[k];
            }
            k++;
        }
    }

    // Loop to generate
    // encrypted let
    for (let j = 0; j < b; j++) {
        for (let i = 0; i < a; i++) {
            encrypted = encrypted +
                arr[i][j];
        }
    }
    return encrypted;
}

// Function to decrypt the let
function decryption(s) {
    let l = s.length;
    let b = Math.ceil(Math.sqrt(l));
    let a = Math.floor(Math.sqrt(l));
    let decrypted = '';

    // Matrix to generate the
    // Encrypted let
    let arr = new Array();
    for (let i = 0; i < a; i++) {
        let temp = [];
        for (let j = 0; j < b; j++) {
            temp.push([])
        }
        arr.push(temp)
    }
    for (let i = 0; i < a; i++) {
        for (let j = 0; j < b; j++) {
            arr[i][j] = " "
        }
    }
    let k = 0;

    // Fill the matrix column-wise
    for (let j = 0; j < b; j++) {
        for (let i = 0; i < a; i++) {
            if (k < l) {
                arr[j][i] = s[k];
            }
            k++;
        }
    }

    // Loop to generate
    // decrypted let
    for (let j = 0; j < a; j++) {
        for (let i = 0; i < b; i++) {
            decrypted = decrypted + arr[i][j];
        }
    }
    return decrypted;
}

// Driver Code

let s = "Geeks For Geeks";
let encrypted;
let decrypted;

// Encryption of let
encrypted = encryption(s);
document.write(encrypted + "<br>");

// Decryption of let
decrypted = decryption(encrypted);
document.write(decrypted);

// This code is contributed by gfgking

</script>

Output:

Gsree  keFGskoe 
Geeks For Geeks

Time Complexity: O(?n * ?n) ? O(n)
Auxiliary Space: O(n), where n is the length of the given string.

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